Need some advice on 71 Challenger purchase
Well first off if the 440 is a stock motor home engine it'll be low compression, 8 to 1 or so and will probably have the cast crank in it. At the front of the engine, on top drivers side, across from the distributor hold down clamp you'll find a 2"x1" flat pad cast into the block. Stamped into the pad will be a letter (eg. M = 1976) followed by 440. If the engine runs good they are good engines just not a fire breather and with the right amount of cash can be turned into one. I'll post a link that can tell you what crank is in it just by looking at the crank balancer. If the car doesn't show any obvious cancer be sure to check for bondo on the body just below the rear window in the corners and pull the spare tire and check the wheel well for rust along with the complete underside. Next the rear end, I've heard over the years that the 318 Challengers might come from the factory with 8 1/4" rear ends which that 440 even stock ain't going to like. I'll put a link in that you can tell what it is from the picture either 8 1/4 or 8 3/4". Lastly unless the body has had a recent paint job and the underside is mint no rust I think he's asking about 4K to much after all it is a 318 car.
http://www.moparts.org/Tech/Archive/bb/50.html
http://www.moparts.org/Tech/Archive/axle/6.html
Terry